S-Block Elements
s-Block Elements are the elements belonging to first ad second groups of the periodic table . The differentiating or final electron enters the s orbital in all these elements ; thus they are called as s-block elements . 'Group 1' 'Elements' The elements of the group 1 are Lithium (Li)(3) , Sodium (Na)(11) , Potassium (K)(19) , Rubidium (Rb)(37) , Caesium (Cs)(55) , Francium (Fr)(87) . 'Occurrence' Lithium is the 35th most abundant element in earth's crust and occurs mainly in the forms of Silicates . Sodium is the 7th most abundant element in earth's crust . Potassium is the 8th most abundant element in the earth's crust . Rubidium and Caesium are much less abundant . Francium is Radioactive in nature and extremely rare . 'Electronic Configuration' Gas ns1 Physical State Alkali metals are soft , thus can be cut by knife . Lithium is the hardest alkali metal . Atomic and Ionic Radii The ionic radii of alkali metals are smaller than their corresponding atomic radii e.g. Na+ < Na . The ionic and atomic radii of alkali metals is highest in their respective periods . e.g. Atomic radii of Sodium is highest in Group 3 . The atomic and ionic Radii increases down the group . Density Alkali metals have a low density . Li , Na , K are lighter than water . Density increases down the group . But , Potassium is lighter than Sodium . Density is low because of large size of atoms . As we go down the group , the increase in mass is more than increase in size ... Density increases down the group . Melting and Boiling Points Alkali metals possess low melting and boiling points . The melting and boiling points decrease down the group . As the size of atom increases , the intermolecular force decreases and ... melting and boiling points decrease down the group . NOTE : The melting & boiling points in this case do not depend upon the density of the atoms , but on the extent of intermolecular forces of attraction . ' '''Ionisation Enthalpy ' The ionisation enthalpy of Alkali Metals is very low due to weak bond between valence electron and nucleus . The ionisation enthalpies of Alkali metals are lowest in their respective groups . e.g. Sodium has the lowest ionisaton enthalpy in the Group 3 . The ionisation enthalpy goes on decreasing down the group , as the size of the atom increases and the nuclear charge decreases . The second ionisation enthalpies of Alkali metals are very high because upon losing one electron , the alkali metals gain Noble gas configuration , which is the most stable configuration . '''Electronegativity Alkali metals possess the lowest values of electronegativity after noble gases . Alkali metals are highly electropositive , since thy have a high tendency to donate an electron . Electronegativity decreases down the group , since the tendency to donate electron increases down the group , as the valence electron is losely bonded to the nucleus . Oxidation State All Alkali metals show only +1 oxidation state . Hydration Energy The energy liberated during hydration is called Hydration Energy The Hydration Energy of Alkali Metals decreases down the group . Flame Test Colour of the flame darkens down the group Li = Crimson Na = Golden Yellow K = Pale Violet Rb = Violet Cs = Violet When an alkali metal is heated , its valence electron gets excited , due to energy provided by the heat . But , this excitation is short lived . Soon , the electron gets de-excited and emits energy in the form of light energy (photons) . Photoelectric Effect Alkali metals are highly photosensitive , because they show a high tendency to donate electrons . Light of energy greater than ionisation enthalpy (work function) is needed for photoelectric effect . Nature of Compounds Alkali metals always form ionic compound . Alkali metals are highly electropositive , this factor creates a huge electronegativity difference with the reagent . Lattice Energy of the Compounds Lattice energy is referred to the energy released to form crystal lattice structure of a compound . Alkali metals have a high lattice energy . The lattice energy decreases down the group . Alkali metals form metallic bonds which are bonded together with high electrostatic force of attraction . ... A lot of energy is released during condensation of gas or liquid to crystal lattice structure . Lattice energy decreases with increase in atomic size . ... Lattice Energy decreases down the group . Anomalous Behavior Lithium shows anomalous behaviour and has a diagonal relationship with Magnesium . Important Compounds Sodium : Sodium Carbonate , Sodium Bicarbonate , Sodium Chloride , Sodium Hydroxide Biological Importance Sodium : Major cation in blood plasma , reduction in fat deposits , atrophy of muscles , lung infection , retarded bone growth , reduces blood pressure . Potassium : reduces Heart Beat , scarring of heart muscles , hypertrophy of kidney , paralysis of muscles . Group 2 'Elements' Group 2 elements are called as alkaline earth metals . Berylium (Be)(4) , Magnesium (Mg)(12) , Calcium (Ca)(20) , Strontium (Sr)(38) , Barium (Ba)(56) , Radium (Ra)(88) are the Group 2 Elements . 'Occurrence' Berylium is the 51st most abundant element int he earth's crust . Magnesium is the 6th most abundant element . Calcium is the 5th most abundant element . Strontium and Barium are less abundant . Radium is a radioactive element and very rarely available . Electronic Configuration Gas ns2 Physical State They are more harder than alkali metals . Hardness decreases down the group due to decrease in atomic size . Atomic and Ionic Radii The Atomic radii of Alkaline Earth Metals is less than the corresponding alkali metals . The atomic and ionic radii goes on increasing down the group . Density Alkaline Earth Metals are more dense than alkali metals . The density decreases down the group till Calcium and then sharply increases from Calcium to Barium . The density increases because the increase in mass overweighs the increase in atomic size . The irregular variation down the group is probably due to change in the crystal structure . Alkaline Earth metals are more denser than alkali metals because their mass is more as well as their size is lesser than alkali metals . Melting and Boiling Points ' The Alkaline Earth metals have higher boiling and melting points , due to larger nuclear charge . No regular trend is seen down the group . '''Ionisation Enthalpy ' The Ionisation Enthalpy of alkaline earth metals is more than alkali metals because they possess a larger nuclear charge . The ionisation enthalpy decreases down the group due to increase in atomic size . The second Ionisation enthalpy values for alkaline earth metals is lower than that of alkali metals . This is because the second electron is removed from stable noble gas core in alkali metals , while the second electron is removed from the valence shell in Alkaline Earth metals . 'Electronegativity ' Alkaline earth metals have low electronegativity values , but they are more electronegative than alkali metals . The lower values of electronegativity is due to the electropositive character of alkaline earth metals . Electronegativity decreases down the group , since metallic or electropositive character inreases down the group '''Oxidation State Alkaline Earth Metals show +1 or +2 oxidation state . Nature of Compounds Berylium and Magnesium form only ionic compounds . Higher elements , too mainly form ionic compounds ; but they also form covalent compounds to some extent . Flame Test Calcium Brick Red Strontium Crimson Barium Apple Green Radium Crimson 'Anomalous Behaviour' Berrylium shows anomalous behaviour and has a diagonal relationship with Aluminium . General Properties and uses Category:Chemistry